PhD student Dakrong Pissuwan is part of the team working on nanoparticles that can target disease-causing micro-organisms.Photo by Joanne Saad.

Antibiotics and chemotherapy – two common medical treatments – flood our bodies with toxic pharmaceutical compounds in the hope that they will find and destroy the invasive micro organisms or tumour cells that are making us feel unwell. Unfortunately, the process is not targeted and can cause unintended side-effects in healthy body tissue.

A new means to target disease-causing micro-organisms without damaging the surrounding healthy body tissue has been demonstrated by a team of researchers in the Faculty of Science. This research focuses on the parasitic organism Toxoplasma gondii. Infection with this organism can cause pregnant women to abort, and transmission of the parasite to the foetus can cause mental retardation, blindness, seizures and death. Toxo infections can also have serious consequences for individuals with AIDS or tuberculosis or patients who have recently received organ transplants.

PhD student Dakrong Pissuwan and colleagues in the Faculty of Science have developed functionalised nanoparticles that can target disease-causing micro-organisms specifically. Pissuwan is working with her supervisors Professor Michael Cortie, Director of the Institute for Nanotechnology, and Dr Stella Valenzuela from Department of Medical and Molecular Bioscience in collaboration with Dr Catherine Miller from the Institute of Biological and Infectious Diseases.

The prestigious journal Nano Letters has published a paper by Pissuwan and her colleagues on this work. It is believed to be the first report in the scientific literature describing the use of nanotechnology to target and destroy parasites.

“A nanoparticle is nothing mysterious,” Cortie says, “It is just a very small particle. But the important point is that solitary, independent nanoparticles are exceedingly rare in living systems under normal circumstances. A conspiracy of natural laws combines to ensure that they aggregate in our bodies or in the external environment and soon become quite ordinary microparticles. However, if we can stabilize them, discrete nanoparticles have unique and interesting chemical and physical properties, many of which can be used in bullet medicine or biotechnology. The trick is to coat or functionalize the nanoparticles with some useful molecules that will prevent the nanoparticles aggregating or reacting prematurely.”

Gold nanoparticles, which have several unique physical attributes, are being used in bio-labelling, biosensors, DNA-analyses and as a pharmaceutically active substance. More recently, workers in the USA have investigated how the special optical properties of these particles can be exploited with the use of a laser to selectively deliver a photo-thermal dose to kill cancer cells. However Pissuwan and her colleagues believe they are the first to successfully develop gold nanoparticles coated with antibodies to target invasive pathogens.

“We coated gold nanoparticles with an antibody specific to the Toxoplasmosis gondii organism in the tachyzoite phase, its fastest growing stage,” says Pissuwan. Following this, the nanoparticles were incubated with a culture containing a mixture of live Toxo organisms and host mammal cells. The gold particles attached selectively to the tachyzoites form of the Toxo parasite, which could then be destroyed by exposure to a low power laser light tuned to the optical resonance of the gold nanoparticles.

Pissuwan says, “To destroy the parasite in the human body will require exposure to a higher intensity laser, but our work has shown that the idea is feasible.” This project provides exciting new possibilities for treatment of pathogenic parasites in general, and the principle could be readily extended to target other organisms, such as those that cause malaria.